1. Field of the Invention
This invention relates to a logic circuit which is typically a combination of a complementary metal oxide semiconductor (CMOS) and a bipolar transistor. The combination will be called a bi-CMOS logic circuit throughout the specification.
2. Description of the Prior Arts
A conventional bi-CMOS logic circuit is disclosed in Japanese Patent Publication (Kokai or Prepublication of Unexamined Patent Application) No. 42614/1987. In the manner which will presently be described, the bi-CMOS logic circuit comprises an input terminal, an input circuit, an output circuit, and a control circuit.
The input terminal is supplied with an input signal. The input circuit has a local terminal and is connected to the input terminal for producing a local signal in response to the input signal to supply the local signal to the local terminal. The output circuit has an output terminal and is connected to the input and the local terminals for producing an output signal in response to the input and the local signals to supply the output signal to the output terminal. In the manner known in the art, the output signal has an output level which is a selected one of a high level and a low level. The control circuit is connected to the input, the local, and the output terminals for controlling the local signal in response to the input and the output signals.
The bi-CMOS logic circuit has, in a first case where the output level is shifted from the low level to the high level, a first operation speed or a first transition speed and, in a second case where the output level is shifted from the high level to the low level, a second operation speed or a second transition speed. In the manner known in the art, it is readily possible in the bi-CMOS logic circuit to increase the first transition speed.
As will later be described in detail with reference to the drawing, however, it is difficult in the bi-CMOS logic circuit to increase the second transition speed and to save current consumption during transition of the output level from the high level to the low level.